Rarity has her Rump Tested
by mdevaughnc
Summary: Twilight is conducting a study on the physical resistance of unicorns. Rarity agrees to help her. She, and her rear end, would soon regret that decision.
1. Chapter 1

Twilight paced back and forth inside her throne room. She recently finished her latest research tool, but she had no test subject. Twilight never enjoyed using live subjects, but what could she do? A live specimen was necessary, it simply couldn't be avoided. And she couldn't let the potential information go to rest, the research had the potential to benefit ponies for years to come. One way or another, Twilight would have to find somepony to use. More than likely, it would have to be one of her friends.

Twilight sat on her designated throne and pondered who would be the best pony to ask. It sadly had to be a pony, because she was certain Spike would volunteer if asked. Pinkie pie was automatically out, she was too much of an outlier. Twilight couldn't tell which results were from the test and which were just Pinkie being strange. Fluttershy would never go for it. Rainbow Dash would likely agree if Twilight dared her to, but she would try to act tough and likely throw off the data. Applejack might say yes, but her Twilight really did not wish to ask her. Her job required intense physical activity. Twilight wouldn't want Applejack to miss any work because he body was too damaged from test. Thus, the only pony left to ask was…

"Twilight! Are you here?"

As if on cue, Rarity galloped through the throne room doors. She saw twilight on her seat and smiled widely.

"There you are! I just had to thank you so much for helping me land the clothing deal with Saddle Arabians."

Three days prior, Twilight and her fellow princesses meet with dignitaries from Saddle Arabia. At one point in the conversion, the female ambassador mentioned that ponies from her land raving over Sapphire Shores's outfit from her latest concert. Twilight then mentioned that it was her friend Rarity who made those outfits. One thing led to another, and the meeting ended with the dignitaries agreeing to contact Rarity about making some outfits in the Saddle Arabian style to sell in their stores.

"I'm guessing they contacted you?"

"Spikey-poo just showed me the letter! They've agreed to pay for a whole line! Can you believe it, my work will be in stores from the other side of Equestria!"

Rarity bounced to Twilight and embraced her in a tight hug.

"Oh thank you, thank you, thank you Twilight! You done me the greatest favor possible! Oh, if there is anything I can do to thank you, please let me know! I mean it, absolutely anything!"

Twilight returned Rarity's hug and looked Rarity in her blue eyes.

"Oh Rarity, you don't need to thank me. You got that line based on your own merit. I don't deserve any credit."

"Nonsense! You were an enormous help! I simply must pay you back. Surely there must be something I can help you with, anything!"

Twilight scrunched her face and turned her eyes away. "Well, there might be something…"

Rarity let out a chuckle. "I knew it! Whatever it is, you have my assistance."

"Rarity, you don't even know what it is yet."

"It doesn't matter, darling. I will put in my best effort to aid you, regardless of the task. You have my word."

"...do you really mean that?"

Rarity placed a hoof on Twilight's shoulder. "By Celestia's mane, I do."

Twilight smiled warmly and sighed. "Ok then. I actually do have a problem, and I was actually considering asking you anyway."

Rarity sat down on the diamond throne and crossed her forelegs rested her head on them.

"I'm all ears. What do you need help with?"

Twilight returned back to her own seat and closed her eyes before recanting. "As you know, we and our friends tend to get into a handful of fight."

"More than most ponies go through in a lifetime."

"Exactly. And with our new castle and my new status, we will most likely encounter even more fights. So I figured that it's in our best interest to have some extra protection."

Rarity nodded. "That would be nice."

"Right. So for the past week, I've had Cadence help me adapt her 'protection bubble' spell. I picture I can alter it from shield my to creating personal barriers around all of us."

"Oh! That sounds most impressive!"

"Thanks! So, I've been practicing the spell on myself for the a while. All was going while, until I found out an error."

"An error? Like What?"

Twilight blushed and turned her face to the side. "The spell provides adequate protection over a ponies body, except for a certain… part."

"Certain part?"

"The spell is too weak on a certain body part. A lower body part."

Rarity blinked in confusion. "Lower body? You mean the legs?"

"Noooo."

"The back?"

"Close. A bit further down."

"Further down. You don't mean the…" Rarity noticed Twilight's rosy cheeks, which affirmed her thoughts."

"...you mean the flank, don't you?"

Twilight didn't face Rarity but nodded. "That's correct. For some reason, the barrier around the flank is too weak. It barely provides any protection."

Rarity looked at her friend with slanted eyes as she began to work out what help Twilight was asking for. "So when you say you need help…"

"I mean I need to make use of your hindquarters. That would be the gist of it."

"...Oh" was all Rarity could respond. Knowing Twilight, she was prepared for an odd request, but this took the cake. Twilight wants to make use of flank? To do what with it?

Twilight coughed into her hoof and continued. "Obviously, the key to fixing this problem is gather more information about that area of a pony under strenuous actions to further alter the barrier."

"...um, can you translate that into layman's terms darling?"

"I would need to perform stress test on your rear end."

Rarity never imagined hearing that sentence. "What… kind of test?"

Twilight turned back around at the chance to explain something. "Basically, I would perform particular actions on your rump and record your reactions."

Rarity raised her eyebrows. "What kind of reactions."

Twilight again turned away from Rarity. "Your… level of pain."

"PAIN!" Rarity shouted. "Why would I be in pain?!"

Twilight recoiled back from the outburst. She held up her front hooves in front of her face."I'm sorry! I'm sorry! But for the test to be practical, we'll have to make the test strenuous on your flank! The barrier needs to be able to protect from hard hits, therefore your flank has to be hit hard."

Rarity's pupils shrunk into her eyes. She meeked out in a quiet voice, "hit? you plan to hit my flank?"

Another sigh. "Yes. I broke the tests into three parts to test the range of resistance: a hard edged force, a hoof strike with an instrument, and a puncture force.

Rarity gulped. Beads of sweat slid down her face. "And in what way to do you intend to test these parts."

Twilight finally grew the courage to look Rarity in her face to answer. "By spanking you, kicking your flank with a boot, and hitting your behind with a miniature cactus."

Five minutes later, Rarity awoke laying on a pile of pillows. She was covered by a purple blanket and felt a cool breeze fanning her. She looked up and saw Twilight levitating a fan to blow on her.

"How do you feel, Rarity?"

Rarity opened her eyes and stretched out her legs. "I feel fine, darling? Um, why am I laying down on this dirty floor."

"Sorry, I didn't want to move you after you fainted, so I just placed the pillows under you."

"Fainted?"

Twilight gulped again. "Yes. You passed out after I explained the resistance test to you."

The conversation flooded back to Rarity. "Oh yes, I remember now. There was talk of spanking and kicking and…."

"And a cactus."

"Oh yes, and a cactus." Rarity nerves returned. "And I assume these tests are absolutely necessary."

Another sigh. "I'm afraid so. This barrier is very important to me. I can't bear the thought of my friends in danger when there is something I can do to help them. This shield could potentially save one of our lives. Besides that, other unicorns could research the spell and use it themselves. This has the potential to revolutionize defense measures for years!"

By now, Rarity was used to Twilight's enthusiasm towards scientific discovery, but she was still amazed by her friends determination. She always worked hard to help others, even as a princess. Twilight was always there for her friends, so it's only fair that her friends return the favor.

"This is important to you, isn't it darling?"

"Very. I really, really want this to work out."

Rarity shut her eyes and took a deep breath. Sh breathed out the last of her hesitations.

"Ok then. I will help you."

Twilight's eyes filled with stars. "Really?! Do you really mean it, Rarity?!"

"I do. If it's to help you and our friends, a little… posterior pain is worth it. I'm in."

"Oh thank you Rarity!" Twilight said as she embraced her unicorn friend. "Trusts me, this won't take long. We can finish it today, in fact!"

"Really? That quickly?"

"Oh yes! I just need to inflict pain on your rear end and chart your reaction. Easy!"

Rarity gave a dry chuckle. "Well if that's all, then I guess the sooner this is done the better. Let's begin."

Twilight clapped her two hooves together. "Great! I just have to do one thing." A purple light temporarily blinded Rarity as Twilight teleported behind her. She then squeaked as Twilight ran a hoof over her flank, down the diamonds on her side.

Rarity blushed and stammered, "Twi-Twilight! What are you doing?!"

"Before the tests, I need to understand the body part, to build a baseline. It won't take long."

With that, Twilight inspected Rarity rear with her patented scrutiny. She ran her hooves up and down her sides, taking time to trace slowly trace her cutie marks. Twilight brought her face closer and rubbed her cheek on Rarity's cheek. Then she moved her bottom flesh around, noting how the flesh bounced and ebbed.

Rarity stood still during the inspection, but shivers shot throughout her body. The only time a pony paid so much attention to her flanks were at the spa. Twilight's such touch and care gave the two a run for their money. She closed her eyes and soaked in Twilight's pokes and prods. Maybe these tests weren't so bad, if they led to more of this.

"All most done, Rarity. Just one more thing."

"Oh, take your time darling. Honestly, I rather enjoy the… AHHH!" Rarity shouted when she felt cold, wet sensation on her flank. She turned around to see Twilight licking her rump.

"Is-is this really necessary, Twilight."

"Of course. There's no such thing as unnecessary data. We need to gauge all the aspects of your rear, including taste." Twilight returned to her task and slurped Rarity butt. IT was if Rarity's flank was an ice cream as Twilight dragged her tongue up, down, and around the rump. She took extra care to swirl her tongue on her diamonds, earning soft moans from Rarity.

To finish up, Twilight puckered her lips and kissed the rump.

*pop*

A light sound was heard as planted kiss after kiss on the bottom. Rarity's legs were beginning to buckle from the attention, so Twilight placed her hooves on both ends of her posterior to steady Rarity. She continued smooching Rarity's butt.

*pop*

*pop*

*pop* *pop* *pop*

With one last kiss, Twilight let go of Rarity. The unicorn was going to collapse but Twilight caught her in a purple aura. Twilight wiped her mouth and went around to face Rarity.

"Are you feeling ok, Rarity?" Twilight asked.

Rarity took a moment to compose herself from her blissful state. "Oh, yes. That was quite the experience. I think I may want to pursue a career in the sciences myself."

Twilight giggled, "Good to hear." But he smile faded and her face turned to gloom. "Truth be told, that wasn't for research. I just wanted to make you feel good before we start. Because trust me, the next experience will be far from pleasurable."


	2. Stage 1: Spanking

Twilight waited for Rarity to recover from her "inspection". Rarity was still shivering from the experience. It had been a few moons since her last intimate experience, and it hadn't involved such attention to her rear end. She made a note to try it more in the future.

Twilight turned to Rarity. "Are you ready to start, Rarity?"

Rarity sighed. "I guess so. The sooner we begin, the sooner this is over? Let's get started."

Twilight nodded and lit up her horn. With a purple flash, the two ponies were teleported to spacious room, padded with yellow insulation. The room was pretty bare, only containing a work desk with a console on the table, and a purple, two seat couch.

"Where are we?" Rarity inquired.

"We're still inside the castle, on one of the bottom floors. I figured this would be the most private place in Ponyville. I made sure to insulate the walls so nopony could hear us."

"Is this it? It seems pretty barren."

"Well, I've been told that my experiments tend to become too outlandish and extravagant. This time, I took the simple approach and only brought the essential tools. ".

"Well then, where are they? I don't see anything else here?"

Twilight walked over to the bench and sat down. "I think it would easier to just show you. You'll understand once we start."

Twilight pointed a hoof to the end of the couch. "If you would kindly get the end of the couch, with your posterior pointing into the air, then we can begin."

Rarity wasn't sure what was going to happen, but she never less compelled. She hopped onto the couch and laid her head on the cushion. She moved her back legs over the edge and stuck her rear in the air. Her cheeks marooned at how vulnerable her position left here.

Rarity left out a held breath. "Okay, darling. I am in position. Now what do I do?"

Twilight responded by magically opening a drawer and levitating lengths of gray rope. "Try not to freak out."

"Freak out from wh..." Rarity was cut off when Twilight began wrapping Rarity in the rope. With a moment of practiced movements, Twilight finished tying Rarity down. The ivory unicorn was now entangled, strapped to the couch by numerous coils around her body. Her flank was still hitched high off the end.

Rarity turned a bit livid. "Twilight! What the hay is this?! Untangled me this instance!"

Twilight solemnly shook her head. "No can do, Rarity. It's imperative that once we begin, you can't quit and try to flee. We need to make sure you stay put."

Rarity's annoyance bled out into panic. "This is really so necessary? Just how bad is this ordeal going to be?"

Twilight said nothing, just fiddled back into the drawer. What see took out next scared Rarity more than any foe she ever faced.

Twilight has levitating a foot long, wooden spanking paddle. Rarity had a novice knowledge of bdsm and noticed the eight small holes drilled in were meant to decrease air flow. Meaning the spanking could have that much more force.

Rarity gulped at the sight. "I-I-I assume that is the first instrument to be used in these tests?"

Twilight nodded, her eyes closed in regret. "That's correct. It should provide ample damage to your buttocks. This particular item is famous in fetish circles for leaving quite a mark."

"I'm so glad you did your research.", Rarity deadpanned. "Wouldn't want to be savagely beaten by inferior devices."

Twilight couldn't chide Rarity for her attitude. She was going to have plenty reasons to be upset. "Yes. Yes. This tool will be more than adequate. So let's get to it then."

With that, Twilight took position behind the couch. Her vision filled with Rarity's big behind. At this angle, Twilight observed how massive Rarity's flank looked. Tying her to the couch had the effect of ballooning her rear. A fluffy white pillow, and just as soft. Twilight recalled how soft and marshmallowy it felt. Such a shame to ruin such a splendid rump.

But Twilight keep her mind on the end result. For the sake of her friends, Twilight calmed down and prepared herself. She took one last deep breath and aimed the paddle. She closed in on Rarity's sit spot and flung.

***WHAP!***

"AAAH!" Rarity cried out from the hit. The impact sent ripples through her rear and spread on the sting. If not for the rope, Rarity would have involuntarily jumped off the couch.

"Good Heavens, Twilight! They hurt!"

"That's the point, Rarity. The test must be painful. Very painful." She took aim again.

***WHAP!***

"Ow! Darn it!" Rarity hissed from the blow. She was already was not used to violence she had absolutely no experience taking a spanking. Never mind a spanking from a bucking Alicorn!

Twilight tried to reassure her friend. "Remember, the room is sound proofed. Feel free to yell out. Studies have shown that yelling can dull the pain."

"Oh, thank you for the advice, Twilight! You're even so kind!"

Twilight simply brushed off the aggression and swung once more, aiming for her cutie marks.

***WHAP!***

"Ouch!" Rarity wanted to move her flank around the ease the pain, but then remembered she was trapped on the couch. She forced to use sit there and be beaten. Rarity chose to instead focus on anticipating each...

***WHAP!***

"Hey! That strike was too fast!"

Twilight shook her head. "Sorry Rarity. I'm afraid you can't anticipate the hits. They need to be..."

***WHAP!*** "EEP!"

"at random intervals. And at different intensities." At that, Twilight increased the force of her magic and swung at Rarity's haunches.

***WHAP!***

"OOWW!" Rarity screamed.

***WHAP!***

"Sweet Celestia!"

Twilight swung twice. ***WHAP!*** ***WHAP!***

"BUCK!" Rarity rarely cursed, but she couldn't keep up her proper role. The pain in her flanks was just too excruciating. Every time her heart beat, her ass would throb. She could feel her white coat becoming rosy.

***WHAP!*** ***WHAP!***

And Twilight was holding nothing back. From foal hood, she took her research seriously. She made sure each crack gave Rarity a hard sting.

***WHAP!*** "OWWW!

Twilight alternated locations, never hitting the same part of flesh twice.

***WHAP!**WHAP!*** "DAMMIT TWILIGHT!"

She made sure to hit the bottom of her rump, where her thighs began.

***WHAP!***

She noticed Rarity reacted most violently when Twilight stuck her sit spot, so made sure to test that spot.

***WHAP!**WHAP!***

"OW! SURELY THIS IS ENOUGH NOW!"

"Not yet"

***WHAP!***

"But we are almost done."

***WHAP!***

"BUCKING HELL!". Rarity was crying yet, but her eyes began to water. The hits were so infrequent and changing intensities, she couldn't take this. Everything hurt her ass. Even the air hitting her bruised rump stung.

***WHAP!***

"HMMMPH!" By this point, Rarity dove her head into the cushions. She closed her eyes and just waited for this horrible paddling to end.

***WHAP!**WHAP!**WHAP!***

At the last hit, Twilight halted. She took note of how red Rarity's rump was. The color reminded her of ketchup, a red stain on a white canvas. She knew Rarity was suffering, but she couldn't stop now. Twilight knelt down to the Rarity's head and spoke to her.

"Rarity, we're almost finished the first part. However, this last part is going to be the hardest. The spanks will be a constant stream, with all my force. Please hang in there, it's almost over."

Twilight received no answer.

"Did you here me Rarity?"

Still nothing.

"Rarity?"

"JUST HURRY UP AND FINISH!" Rarity shouted from the cushions. She didn't want to talk, she wanted to be done already.

Twilight recoiled from the yell. She truly felt for the unicorn. This hard to be the most painful experience she ever faced. She promised herself she would make it up to Rarity later.

Twilight walked back into position. She channeled all her might into the paddle and to aim.

***WHAP!**WHAP!**WHAP!**WHAP!**WHAP!***

Twilight rained down blows upon Rarity's derriere. No breaks, no halts, no holding back. The paddle whistled as it flew through the air.

***WHAP!**WHAP!**WHAP!**WHAP!**WHAP!***

"MMMMMMMMPH!" Rarity didn't have time to screamed, just let loose a continuous moan into the cushions. Her body rocked forward at each hit.

***WHAP!**WHAP!**WHAP!**WHAP!**WHAP!***

For the next thirty seconds, the room shook with the sound of wood on flesh and Rarity's yell of pain. Twilight remained silent. She had to seriously tenderize Rarity, with all her concentration.

***WHAP!**WHAP!**WHAP!**WHAP!**WHAP!**WHAP!***

"And we're done." Twilight said. She floated the paddle to the foot of the desk. She step back and took notice of the results. Rarity's white fur was painted red, expect for the white patches where the holes connected. Twilight could feel the heat radiating from the battered rear end. She knew the flesh underneath the fur must be blood red right now.

Rarity still wasn't sobbing, but sniffling into the cushion. The pain was unimaginable. She thought she could mentally prepare for the spanking, but the reality was far from the truth. Twilight put her through the worst experience of her life. Every injury palled in comparison to the spanking, to the_beating_. She knew she have nightmares of this for weeks.

Twilight sat on the floor next to Rarity's head. "How are you holding out?"

Rarity finished sniffling and answered, "Well, I survived if nothing else. But my goodness, that was horrendous! You tortured me, Twilight! Tortured me!"

"I know, I know. I sorry it had to be that way."

"This damn barrier had better be the best in equestrian history!"

"I hope you realize how much I appreciate this. I would never do this to you without a clear purpose. Please know that."

Rarity sighed. "I know, darling. Let's just..., forget this terrible ordeal and move on."

Twilight managed a smile. "Good to hear. One test down, two to go."


End file.
